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Human population reduction is not a quick fix for environmental problems

Citation

Bradshaw, CJA and Brook, BW, Human population reduction is not a quick fix for environmental problems, National Academy of Sciences of The United States of America. Proceedings, 111, (46) pp. 16610-16615. ISSN 0027-8424 (2014) [Refereed Article]

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Abstract

The inexorable demographic momentum of the global human
population is rapidly eroding Earth’s life-support system. There are
consequently more frequent calls to address environmental problems
by advocating further reductions in human fertility. To examine
how quickly this could lead to a smaller human population, we
used scenario-based matrix modeling to project the global population
to the year 2100. Assuming a continuation of current trends in
mortality reduction, even a rapid transition to a worldwide one child
policy leads to a population similar to today’s by 2100. Even
a catastrophic mass mortality event of 2 billion deaths over a hypothetical
5-y window in the mid-21st century would still yield around
8.5 billion people by 2100. In the absence of catastrophe or large
fertility reductions (to fewer than two children per female worldwide),
the greatest threats to ecosystems—as measured by regional
projections within the 35 global Biodiversity Hotspots—indicate
that Africa and South Asia will experience the greatest human pressures
on future ecosystems. Humanity’s large demographic momentum
means that there are no easy policy levers to change the size of
the human population substantially over coming decades, short of
extreme and rapid reductions in female fertility; it will take centuries,
and the long-term target remains unclear. However, some reduction
could be achieved by midcentury and lead to hundreds of
millions fewer people to feed. More immediate results for sustainability
would emerge from policies and technologies that reverse
rising consumption of natural resources.